Germany may be known for thoroughness, but when it comes to tracing the ownership of art stolen by the Nazis, its experts are - apparently - far too slow.

Ronald S Lauder, head of the World Jewish Congress, delivered a scathing verdict last week on Germany's efforts to ferret out the history of some 1,000 works in art hoarder Cornelius Gurlitt's infamous collection, which German tax investigators found in 2012.

So far, the German researchers have found only five works in the trove that were clearly stolen or confiscated by the Nazis.

Mr Lauder, an art collector himself, decried "the failures throughout the process… the persistent lack of transparency and communication" and said he "expected Germany to do better, given that time is running out".

The task force was set up two years ago. In the meantime, hundreds of claims from potential heirs have poured in. The team's work will now be taken up by the Magdeburg-based Centre for Lost Cultural Goods, a government agency.

In defence of their progress, task force chair Ingeborg Berggreen-Merkel said that the team of researchers was committed to seeking justice for victims of Nazi crimes and their families, and that this took time.

So far, two works have been returned to different heirs - one by Henri Matisse and one by Max Liebermann.

Gurlitt's father, the art collector Hildebrand Gurlitt, procured artworks on assignment for high-level Nazis who wanted to stock museums in the Reich or sell the works for profit. Out of about 1,500 works, some 500 were not investigated since they were either made by Gurlitt family members or were created after the Second World War.

Culture Minister Monika Grütters said last week that data on 200 works already researched will be published online along with the correspondence of Hildebrand Gurlitt.

Cornelius Gurlitt died in 2014 and left the collection exclusively to the Art Museum Bern Foundation in Switzerland. A cousin has challenged the will in a Munich court.